The present invention relates to a transfer device incorporated in an image forming apparatus for performing a primary transfer of developer images from a plurality of image bearing members arranged side by side onto an intermediate transfer belt and then performing a secondary transfer of the developer images from the intermediate transfer belt onto a recording medium. The present invention also relates to an image forming apparatus incorporating such a transfer device.
A tandem type full-color image forming apparatus having a plurality of image bearing members includes a transfer device configured to transfer an image onto a recording medium via an intermediate transfer belt. The transfer device is incorporated in the image forming apparatus in such a manner that a predetermined region of the outer peripheral surface of the intermediate transfer belt is opposed to the plurality of image bearing members. The transfer device includes a plurality of transfer members opposed to the respective image bearing members across the intermediate transfer belt. In a conventional transfer device having the transfer members located offset from the respective image bearing members, all the transfer members are offset downstream from the respective image bearing members in the moving direction of the intermediate transfer belt (see Japanese Patent Laid-Open Publication No. 2008-009011 for example).
Such a transfer device is designed such that in monochrome image formation a monochrome image transfer member assumes its pressing position while color image transfer members assume their separating positions. Thus, the intermediate transfer belt is brought into contact with the monochrome image bearing member while being separated from the color image bearing members. In full-color image formation, on the other hand, all the transfer members assume their respective pressing positions. Thus, the intermediate transfer belt is brought into contact with all the image bearing members.
In this way, the transfer members move in a direction such as to press the intermediate transfer belt against the image bearing members or in a direction such as to separate the intermediate transfer belt from the image bearing members so as to meet the monochrome image formation and the full-color image formation.
In recent years, demands exist for downsizing of image forming apparatuses. One of such demands is for downsizing of the transfer device in the moving direction of the intermediate transfer belt.
With the conventional transfer device, however, when the spacing is reduced between first and second entraining rollers about which the intermediate transfer belt is entrained in order to downsize the transfer device in the moving direction of the intermediate transfer belt, the spacing between that transfer member which is located at one end in the moving direction of the intermediate transfer belt and the adjacent one of the first and second entraining rollers and the spacing between that transfer member which is located at the other end in the moving direction of the intermediate transfer belt and the adjacent one of the first and second entraining rollers, are also reduced. For this reason, each of the transfer members located at opposite ends in the moving direction of the intermediate transfer belt might collide with a respective one of the first and second entraining rollers when the transfer members move in such a manner as to meet the monochrome image formation or the full-color image formation.
A feature of the present invention is to provide a transfer device and an image forming apparatus, both of which can be downsized in the moving direction of the intermediate transfer belt.